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Here is the BEST Time to Start Onion Seeds in Wisconsin (2023)

Do you want to grow onion seeds in Wisconsin, but don’t know when to start them?

growing seeds

Whether growing indoors or in a garden, starting onion seeds is not as easy as it seems.

Here’s why:

  • Onion Seeds must be consistently watered, receive at least 8 hours of sunlight a day, & be kept at room temperature of at least 70 degrees Fahrenheit.

So if you don’t consistently water them they won’t germinate. If they aren’t in a room that is at least 70 degrees Fahrenheit they won’t sprout. And if it receives 8 hours of sunlight the plant itself won’t grow.

  • Because Wisconsin’s growing season is not long enough, onion seeds cannot be sowed outside and should only be started indoors.

Because of this, I’m going to teach you the ideal time to start onion seeds indoors in Wisconsin:

  • To Learn More About HOW to Grow Onions, Check Out This GUIDE!


When to Start Onion Seeds Indoors

Depending on the type of onions, it takes roughly 40-60 days (6 to 8 weeks) to grow onions from seed indoors before you can transplant them into your garden.

The approximate date of when you should start your onion seeds indoors can be found by:

  • Finding the last average frost date HERE
  • And then subtract 60 days from it

You can also find the average last frost date for most major cities in the below chart that I have created:

wisconsin frost dates

To help ensure the greatest success of your onion seeds germinating you should:

  • Use a heat mat to ensure the gardening pot remains at 70 degrees Fahrenheit
  • Use a grow light to control how much light your onion seeds receive
  • Water your seeds with a spray bottle to ensure your seeds are not overwatered

Once your seedlings are ready, you can read how to transplant your plant HERE.

It should also be noted that you will not want to introduce your onion plants into your garden until 2 weeks after your last frost or else your plant will potentially die or not bear vegetables.

If you want to learn WHEN to start ANY Vegetable Seed in Wisconsin, head over to HERE and just type in the vegetable you want to grow.

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